Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical wireless network includes a number of base stations each radiating to provide coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices. In turn, each base station may be coupled with a switch or gateway that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, such a network may operate in accordance with a particular radio access protocol, examples of which include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), BLUETOOTH, and others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between base station coverage areas, and other functions.
Each base station may provide wireless service to UEs on one or more carrier frequencies (carriers), each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), defining a frequency channel multiplexed over time between downlink and uplink use. Each carrier or its respective channels could be within a defined frequency band and could be of a particular frequency bandwidth, such as 5 MHz, 10 MHz, or 20 MHz for instance, defining a certain extent of air interface resources. A given base station could be arranged to serve a UE on a single such carrier at a time or, with carrier aggregation service or the like, on multiple such carriers at a time.
On each carrier frequency in a coverage area, the coverage area may also define a number of air interface channels for carrying information between the base station and the UEs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing, for instance. By way of example, each coverage area may define a pilot channel, reference channel or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that UEs may detect as an indication of coverage and may measure to evaluate coverage strength. As another example, each coverage area may define an uplink control channel or other resource on which UEs may transmit control messages such as registration requests and access requests to the base station. And each coverage area may define a downlink control channel or other resource on which the base station may transmit control messages such as system information messages and page messages to UEs. Each coverage area may then define one or more traffic channels or other resources for carrying communication traffic such as voice data and other data between the base station and UEs.
When a UE first powers on or enters into coverage of the network, the UE may scan for and identify a strongest pilot or reference signal and may register with the network by transmitting a registration request or attach request to a base station providing that signal. This registration process may serve to notify the network of the UE's presence in a particular coverage area and to facilitate network authentication of the UE. Once registered, the UE may then operate in an idle mode in which the UE monitors a downlink control channel to receive overhead information and to check for any page messages. In the idle mode, the UE may have no assigned traffic channel resources on which to engage in bearer communication.
When the network has a communication (such as a voice call or other traffic) to provide to a UE that is registered with the network but is operating in the idle mode, the network may page the UE in an effort to then facilitate assigning traffic channel resources to the UE. In particular, the network may transmit on the downlink a page message addressed to the UE. Assuming the UE receives this page message, the UE may then transmit to the network a page response message on the uplink. And upon receipt of the page response message, the network may then assign traffic channel resources to the UE, for use to carry the communication, thus transitioning the UE to a connected or active mode in which the UE can engage in the communication.
Likewise, when an idle UE seeks to initiate a communication (such as to place a voice call or engage in other bearer communication), the UE may transmit on the uplink to the base station an origination or connection request, and the network may then assign traffic channel resources to the UE for use to carry the communication, similarly transitioning the UE to a connected or active mode in which the UE can engage in the communication.
In normal operation, when a base station operates in such a wireless network, the base station may thus engage in various types of communication with other network entities. Such communication could be categorized into “control-plane communication” and “user-plane communication”. The control-plane communication encompasses any of the base station's control signaling with other core network entities to help manage operations in the wireless network and service of UEs, and could thus include communications such as bearer setup signaling, tracking area update signaling, paging, handover signaling, and the like. Whereas, the user-plane communication encompasses bearer data being communicated to or from one or more UEs served by the base station, such as packet data that the base station receives from a gateway system and then schedules/transmits to a UE and packet data that the base station receives from a UE and forwards to a gateway system for transmission on a transport network.
In systems that provide service under more than one air interface protocol, service providers may implement functionality that allows UEs to operate by default on one air interface protocol and to dynamically switch over to operate on another air interface protocol when necessary to engage in certain communications. By way of example, in a system that supports both LTE service for mobile broadband and an older protocol such as CDMA or GSM for traditional voice calls, service providers may implement “circuit switched fallback” (CSFB) functionality, which allows UEs to operate by default on LTE and to switch over to operate on the older protocol to engage in voice calls. Further, service providers may implement “enhanced circuit switched fallback” (eCSFB) functionality to make use of certain additional functions that support transition of a UE from operating on one network to another.
Under CSFB, for instance, a hybrid CDMA/LTE UE may be arranged by default to scan for and register with an LTE network and to operate with its CDMA radio powered off, but to then engage in control signaling with the CDMA network via the LTE network, i.e., over the LTE air interface. To facilitate this, when the UE registers with the LTE network, LTE network infrastructure such as a mobility management entity (MME) may signal through an interworking server (IWS) with the CDMA network to register the UE with the CDMA network as well.
In turn, when the CDMA network has a voice call to connect to the UE, the CDMA network may signal through the IWS to the LTE network to cause the LTE network to transmit a CSFB page message to the UE over the LTE air interface. After further CSFB signaling through the LTE network, the UE may then power on its CDMA radio and tune to the CDMA network to engage in the call over the CDMA air interface.
Optimally, a wireless service provider will strategically implement base stations throughout a market area so that served UEs can move between the base station coverage areas without loss of coverage. Each base station may include an antenna structure and associated equipment, and the wireless service provider may connect the base station by a landline cable (e.g., a T1 line) with the service provider's network infrastructure to enable the base station to communicate with a signaling controller (e.g., MME), gateway system, other base stations, and the like.
In practice, however, it may be impractical for a wireless service provider to run landline connections to base stations in certain locations. For instance, where a service provider seeks to provide many small coverage areas blanketing a market area or to fill in coverage holes between coverage of other base stations, the service provider may implement many small-cell base stations throughout the market area, but it may be inefficient or undesirable to run landline cables to every one of those small-cell base stations.
To connect a base station with the network infrastructure in such a situation, the wireless service provider may implement a wireless backhaul connection between the base station and another base station of the service provider's network. In this situation, the base station at issue operates as a relay base station, and the other base station operates as a donor base station. In practice, the relay base station includes or is coupled with a UE, referred to as a relay-UE, and the donor base station then serves the relay-UE in much the same way that the donor base station serves other UEs. Further, the relay base station itself serves UEs, in much the same way that any base station would.